Crystal structures of 3-meth-oxy-4-{[5-(4-meth-oxy-phen-yl)-1,3,4-oxa-diazol-2-yl]meth-oxy}benzo-nitrile and N-(4-{[5-(4-chloro-phen-yl)-1,3,4-oxa-diazol-2-yl]meth-oxy}phen-yl)acetamide.

The title compounds, C(18)H(15)N(3)O(4) and C(17)H(14)ClN(3)O(3), are heterocyclic 1,3,4-oxa-diazole derivatives which differ from each other in the groups attached to the carbon atoms: a meth-oxy-phenyl ring and a benzo-nitrile group in (I) and a chloro-phenyl ring and an acetamide group in (II). Short intra-molecular C-H⋯O hydrogen bonds occur in both mol-ecules. The crystal structure of (I) features C-H⋯N hydrogen bonds, while in the crystal structure of (II), N-H⋯N, C-H⋯N and C-H⋯O hydrogen bonds are observed.